1. Field of the Invention
The present invention relates to a linear motion rolling guide unit, which is applied to a variety of relatively moving portions in machine tools and testing equipment and in which a slider is mounted slidable on a track rail with rolling elements interposed therebetween.
2. Description of the Prior Art
In conventional linear motion rolling guide units, the sealing between a track rail and a slider that slides on it is realized by end seals attached to the ends of the slider and under seals attached to the underside of the slider.
There is known a linear motion rolling guide unit with a construction as shown in FIG. 9. This linear motion rolling guide unit mainly comprises a track rail 1 having raceway grooves 9 formed longitudinally on both side walls 8 thereof, and a slider 18 slidably mounted astride the track rail 1. The slider 18 includes a casing 2, which is slidable relative to the track rail 1 and has raceway grooves 7 formed at positions facing the raceway grooves 9 on the track rail 1, a number of balls 4 or rolling elements trapped between the opposing raceway grooves 7 and 9 to allow relative motion between the rail and the casing, and end caps 5 attached to the longitudinal ends of the casing, the longitudinal direction being the sliding direction of the casing 2.
The end cap 5 has an end seal 6 that provides the sealing between the track rail 1 and the slider 18. The casing 2 is provided with under seals 3 for sealing between the casing 2, the longitudinal side wall surfaces 8 of the track rail 1, and the underside of the casing 2.
The slider 18 is mounted astride on the track rail 1 and freely slidable relative to it through a number of balls 4 circulating along the raceway grooves 9 in the track rail 1. The large number of balls 4 are led into a raceway 28 formed between the raceway groove 9 of the track rail 1 and the raceway groove 7 of the casing 2, into a direction changing passage formed in the end cap 6 and from there into a return passage 29 formed parallel to the raceway groove 7 in the casing 2, so that the rolling elements circulate in an endless raceway.
The under seal 3, though it has an advantage of being simple in construction and easily manufactured, also has drawbacks that because the under seal 3 is thin, it is easily deformed by external forces and by positional errors between it and the casing 2 and track rail 1, the casing and track rail having the raceway grooves 7, 9 respectively. Hence, the under seal 3, which is subjected to temperature variations and exposed to lubricants as the slider 18 slides on the track rail 1, might swell and be deformed deteriorating the sealing performance.
Furthermore, when the under seal 3 in the conventional linear motion rolling guide unit is formed of plastics and put in operation for a long period of time, it may be swelled by soaking lubricants. In that case, because the under seal 3 is fixed at its ends to the metallic casing 2 as by screws, it cannot move relative to the casing 2 and is thus deformed. When the under seal 3 is deformed, the contact condition or sealing condition between the under side of the casing 2 and the upper surface of the under seal 3 deteriorates, even deforming the sealing portion. In the conventional linear motion rolling guide unit, when the contact condition between the sealing portion and the side wall surfaces 8 of the track rail 1 deteriorates, the sealing performance, particularly, the capability of preventing foreign substances such as dust from entering the raceways is degraded.
As an example device that tackles the above problem, a linear motion guide bearing disclosed in the Japanese Utility Model No. 121220/1991 may be cited. An under seal device of the linear motion guide bearing has two-pronged projections protruding toward the underside of the slider, the two prongs being undulated in the direction of axis of the under seal and elastically deformable toward each other. The slider has the axial end portions of the underside thereof formed with vertical holes, into which the two-pronged projections of the under seal are fitted, and also with through-holes that intersect the vertical holes perpendicularly and pass through the arm or wing portions of the slider. The two-pronged projection of the under seal is engaged in the through-holes.
Another linear motion rolling guide unit to solve the above problem is disclosed in the Japanese Patent Laid-Open No. 44725/1993. This linear motion rolling guide unit has an engagement portion formed at least at one longitudinal end of the under seal and an engagement hole formed in the underside of the end cap for slidably receiving the engagement portion.
The applicant of this invention previously developed a linear motion rolling guide unit and filed an application for a patent (Japanese Utility Model No. 63565/1992). The previously developed linear motion rolling guide unit is constructed as follows. An under seal comprises a core member made of metal and an elastic sealing member having lip portions secured to the core member. A pair of projections having locking portions are provided to the underside of the end caps in such a way that they extend longitudinally and are spaced apart widthwise from each other. The core member is formed with longitudinally elongate engagement holes whose opposing longitudinal edges are formed as locking detents. The locking portions are elastically deformed to engage the locking detents thereby mounting the under seal to the end caps.
In the above conventional linear motion rolling guide unit, the under seal, though it is simple in construction and easy to manufacture, has problems that the under seal will easily develop positional errors with respect to the casing and track rail having the raceway grooves, that the mounting is not simple, and that it is easily deformed by swelling, thermal stresses or external forces. Over a long period of use, the lip portion that slides in contact with the side wall surfaces of the track rail will be worn out, making the adjustment of the under seal impossible. This requires replacing the under seal to restore a good sealing condition. In this way, the under seal of the conventional linear motion rolling guide unit needs improvements in terms of sealing performance and durability.
Further, with the conventional linear motion rolling guide unit, to improve the sealing performance requires accurate positioning of the locking piece and engagement holes in the mounting portion between the under seal and the end cap. It is also complex and difficult to mount and dismount the under seal to and from the end cap. Another disadvantage of the conventional linear motion rolling guide unit is that when the lip portion of the under seal that is in contact with the side wall surfaces of the track rail is worn out, the engagement condition of the lip portion cannot be adjusted, requiring the under seal to be replaced.